Dagu (大故) refers to a necessary and sufficient cause or condition. The Mohists categorized the causes of things being so into dagu (major cause) and xiaogu (小故minor cause). Dagu inevitably leads to the corresponding consequence, while its absence inevitably leads not to the consequence. To put it simply, dagu must be present, and its presence is enough for the occurrence of events.

With the major cause, events are bound to occur; without it, events definitely will not occur. (Mozi)